Numerical modeling of chaotic behavior for small-scale movements of demersal fishes in coastal water

ABSTRACT:   The presented model involves the application of chaos theory to generate fish movements resulting from environmental stimuli. The model uses three steps within a model neural network such as input stimuli, central decision making and response output resulting in fish movements. The stimuli in the first step include the main abiotic and biotic factors, which could be quantified as an intensity parameter that was then normalized as a ratio between 0 and 1. The decision-making process can be generated using chaos dynamics with the stimuli parameters. The response of fish movements from the output signal representing movement speed and direction of fish can be re-regulated as main movement pattern depending on physiological state or life cycle by third response filtering. The simulation results seen as a movement pattern for sea bream and flounder using this neural chaotic model fitted very well to the observations of fish tracked in the sea by ultrasonic tracking methods. It was also revealed that the fish movement components generated as movement velocity and direction when in tidal flow had similar patterns to those patterns seen in field observations with similar irregular and chaotic variations with time.     

Optomotor response and erratic response: quantitative analysis of fish reaction to towed fishing gears

Fish were observed reacting to moving net panels in tank experiments and in trawl gears towed at sea. Two typical response behaviours of haddock, saithe, mackerel, cod and flatfish to the gear are described as optomotor response and erratic response. These two responses were analysed from TV recordings of the reacting fish and are characterised by time sequences of four parameters: swimming speed, acceleration, angular velocity and distance to the net panel. When fish display stable swimming near the net mouth as in an optomotor response, variations of swimming speed, acceleration and angular velocity are relatively low and regular in their amplitude and period. The erratic response is characterised by large variations in velocity, acceleration and angular velocity and only distance to the towed netting panel, which is positive inside and negative outside, shows progressive change. It is suggested that the fish’s process of deciding between optomotor or erratic response to the gear is based on predictable parameters that describe the stimulus like sound, light level, visibility range and object contrast, combined with the limits describing the abilities of the fish to see, hear and move. The behaviour of the observed parameters suggest that the balance between these factors in a model predicting the outcome might benefit from a form of chaos theory.